Cyclic process for separating aromatic hydrocarbons from a mixture of hydrocarbons



CYCLIG PRDCESS FOR SEPARATING AROIIATIC HYDROCARBONS FROM A MIXTURE OFHYDROCARBONS Y Filed July 18, 1944 2 Sheets-Sheet 1 My 18, 1948. A. E.HlRscl-ILER Erm. 2,441,572,

Patented May 18, 1948 PATENT OFFICE CYCLIC PROCESS FOR SEPARATING ARO-MATIC HYDROCARBONS FROM A MIX- TURE OF HYDROCARBONS Alfred E. Hirschler,Drexel Hill, and Moses Robert Lipkin, Philadelphia, Pa., assignors toSun Oil Company, Philadelphia, Pa., a corporation of New JerseyApplication July 18, 1944, Serial No. 545,446

14 Claims. (Cl. ISB- 147) This invention relates to the separation ofhydrocarbons according to chemical type by selective adsorption andparticularly concerns the separation of aromatics from otherhydrocarbons. More particularly, the invention is directed to a processwherein aromatic constituents of hydrocarbon mixtures boiling within therange of gas oil and -lubricating oil are removed by adsorption on agranular adsorbent material, and the adsorbed aromatics are recoveredand the adsorbent material regenerated for further use by means ofliquid desorbing agents.

The invention has particular utility in the preparation of substantiallyaromatic-free oils such as the so-called "white oils or in theproduction of moderately refined oils having reduced aromatic content,for example, electrical oils and motor oils. The invention also isuseful in the preparation of highly aromatic products oi high molecularweight. In its general applicability, it provides a means of separatinghydrocarbon mixtures derived from petroleum, coal, lignite, shale oil,pitches, tars or like sources and which boil mainly above about 500 F.into relatively non-aromatic and aromatic fractions.

It is known that a complex hydrocarbon mixture such as gas oil orlubricating oil may be separated to an extent according to chemical typeby selective adsorption on certain granular adsorbent materials and itis well recognized that silica gel is one oi the most eiiicientadsorbents for this purpose. It has been generally recognized that theadsorptive ailinity of silica gel and like adsorbents varies with thechemical type of compound in accordance'with the following decreasingorder of adsorbability:

(l) Water. a

(2) Organic polar substances such as alcohols, phenols, ethers and thecorresponding sulfur and nitrogen compounds.

(3) Aromatics.

(4) Olefins.

(5) Naphtlienes.A

(6) Paraiilns.

Thus, oi the main hydrocarbon types comprising .gas oil or lubricatingoil fractions,y aromatics are the most readily adsorbed by silica geland methods of effecting the removal of aromatics by means of silicagelare known to the art. In general these methods comprise contacting thehy- 5 drocarbon charge with silica gel by percolation iiltration toadsorb aromatics, and following this with a desorption step wherein thegel' is contacted with a polar material which is very strongly adsorbed,for instance with water,

l0 methanol or acetone, and which serves to replace the aromatics on thegel. The aromatic hydrocarbons thereby are removed from the gel inadmixture with excess desorbing agent, from which they may be recoveredby distillation, ex-

vlli traction, decantation or the like.

These known methods for removing aromatics have proved to be impracticalfor large scale operation due to certain inherent disadvantages, andconsequently have been used only as an analytical tool. One majordisadvantage in such be reactivated by removal of the polar agent beforeit can be reused for further adsorption of aromatics. Reactivation maybe accomplished by steaming the gel and then blowing it with air at arelatively high temperature, Vbut such procedure has not provedpractical for commercial operation due to the unreasonable length oftime involved in heating a commercial quantity of gel to the temperaturerequired for reactivation and in subsequently cooling it before reuse.Furthermore, the gel when reviviiied in this manner is left in a drycondition, so that when it is further contacted with hydrocarbon chargematerial considerable heat is liberated as heat-ofwetting. This againpresents the problem of heat transfer in each cycle of operation.

In the copending application, Serial No. 501,280, iiled September 4,1943, by one of the present inventors, Moses Robert Lipkin, and whichhas issued as Patent No. 2,398,101, April 9, 1946, there is disclosedand claimed a commercially feasible process for removing aromatics byadsorption on silica gel or adsorbents conforming substantially tosilica gel in adsorptive properties. In this process removal of theadsorbed aromatics from the gel and reactivation of the gel for furtheruse are effected in one step by contacting the used adsorbent with adesorbing agent which is less strongly adsorbed, rather than morestrongly adsorbed, than the aromatics. The desorbing agent is ahydrocarbon or mixture of hydrocarbons selected from the chemicalclasses listed hereinabove as having lower adsorbability on silica gelthan aromatics, viz. paralns, naphthenes and oieiins, and suitably maybe a low boiling aliphatic hydrocarbon such as propane, butane andpentane or petroleum ether. This process thus permits reviviiication ofthe silica gel without heating and substantially eliminatesheat-of-wetting effects.

The process disclosed in the aforesaid application is not, however,generally suitable for the treatment of hydrocarbon fractions which boilabove the kerosene range, such as gas oil or lubricating oil. It hasbeen found that aromatic hydrocarbons present in such higher boilingfractions are, to large extent, suihciently strongly adsorbed by silicagel so that inordinately large amounts of the specified desorbing agentsare required to effect substantial desorption. Presumably this is due toa larger number of aromatic rings per molecule and the presence of morecondensed rings th'an in the aromatics of gasoline or kerosene boilingrange. However, we have now devised a method of removing these higherboiling aromatics substantially completely from theadsorbent and ofreactivating the adsorbent for further use by means of properly chosenliquid desorbing agents. Thus the present process likewise permitsreactivation of the adsorbent without heating and substantiallyeliminates heat-ofwetting effects.

In accordance with the present invention, aromatics are removed from agas oil or lubricating oil charge stock by adsorption on silica gel orother adsorbents of similar nature and the retained aromatics aredesorbed from the adsorbent by means o1' an organic primary liquiddesorbing agent which meets certain requirements with regard toladsorbability, as hereinafter specied. Examples of primary desorbingagents are benzene and ethylene dichloride. For maximum reactivation ofthe adsorbent, this primary de sorbing agent is, in turn, desorbedfromthe gel by means of a secondary desorbing agent of loweradsorbability. The secondary desorbing agent may be of the typespecified in the aforesaid application, Serial No. 501,280, and mayconsist of parailnic, naphthenic as well as olen hydrocarbons which donot polymerize at ordinary temperature in the presence of adsorbentssuch as silica gel, e. g. low boiling hydrocarbons such as propane,butane, isobutane, pentane, isopentane, cyclopentane, hexanes or thelike or mixtures of such hydrocarbons as, for example, pe-

troleum ether, and preferably is an aliphatic or saturated cyclichydrocarbon or a mixture of such hydrocarbons. Low boiling hydrocarbonsare preferable since there appears to be some improvement in desorbingcapacity as molecular weight of the desorbing agent decreases althoughthe use of hydrocarbons of the aforementioned types boiling in or abovethe boiling range of the aromatics in question `are not excluded fromthe scope of the invention. In case it is desired to prepare productswhich are aromatic-free or substantially so, use of the two desorbingagents in consecutive order is required. However, if it lthan are thearomatics.

vagent for its own displacement.

is desired merely to reduce the aromatic content of the charge in orderto produce a moderately rened oil, the gel after treatment with theprimary desorbing agent is in a sufficiently reactivated state for thispurpose so that the step of removing the rst desorbing agent by means ofthe second may be omitted, provided th'e adsorption step is carried outunder certain operating conditions as hereinafter speciiied.

We have found thatl in order not to require an excessive amount o1'desorbing agent in removing the high boiling. aromatics substantiallycompletely from the adsorbent, it is necessary that the primarydesorbing agent be more strongly adsorbed, as deiined below, by theadsorbent We have also found that, even though the secondary desorbingagent is incapable of eecting substantial desorption of the aromaticsunless an excessive amount is used and although the primary desorbingagent is more strongly adsorbed than the aromatics in the particularsense hereinafter speciiied, nevertheless the primary agent, if properlychosen, may be displaced by a reasonable amount of the secondary agent.However, this can be achieved only if the diil'erence in adsorbabilitiesof the two agents is not too great. Thus, the adsorbability of theprimary agent should lie within a rather specific range, beingsuiiiciently high to be e'ective in displacing the aromatics but not sohigh as to require excessive amounts of the secondary Numerous organicliquids meet these requirements and therefore may be used as the primarydesorbing agent. Methods have been devised for ascertaining theadsorbabilities .of a solvent in order to determine its suitability forthis purpose, and these methods are utilized in specifying the primarydesorbing agent in accordance with the invention.

The ability of a primary desorbing agent satisfactorily to desorb thearomatics is ascertained from th`e adsorption isothermv of the aromaticsand solvent in binary mixture. An adsorption isotherm is therelationship between composition of a solution and the amount of acomponent adsorbed by a given mass of adsorbent in equilibrium with thesolution at constant temperature,

more strongly adsorbed than the aromatics, by

which is meant that it will be preferentially adsorbed from binarysolution with the aromatics over at least a major portion of theconcentration range as indicated by the adsorption isotherm. This ldoesnot imply that the primary desorbing agent need be preferentiallyadsorbed at all concentrations. By way of illustration, Fig. 1 of theaccompanying drawings shows adsorption isoth'erms for benzene in binarysolution with lubricating oil aromatics with a silica gel adsorbent atroom temperature. Two curves are shown corresponding to two differentfractions of aromatics used, namely, fraction A which was the mosthighly aromatic material derived from a lubricating oil stock (i. e., itcontained the largest proportion of aromatic rings per molecule) andfraction B which was derived from the same stock but was less aromatic.It may be seen that with fraction A, the type of curve commonly calledan S-shaped curve was obtained, showing that neither benzene nor th'earomatica were preferentially adsorbed over the whole concentrationrange. However, fraction A was preferentially adsorbed only when itsconcentration was below about 11 per cent whereas benzene waspreferentially adsorbed throughout the remainder of the concentrationrange. .Therefore, for the present purpose, it may be said that benzeneis more strongly adsorbed than the aromatics represented by fraction Aand thus that it is suitable for displacing such aromatics from theadsorbent. As further shown in Fig. 1, a so-called U-shaped curve wasobtained with fraction B, indicating that benzene was preferentiallyadsorbed throughout the whole concentration range with these aromaticsand therefore that the latter may be displaced with still smallerproportions oi.' benzene than requiredby fraction A. Any desorbingliquid which, in solution with the aromatics it is to displace, ispreferentially adsorbed throughout more than 50 per cent of theconcentration range is capable of desorbing such aromatics substantiallycompletely, without unreasonably large proportionsof the liquid beingrequired. For indicating the suitability of a given liquid as theprimary desorbing agent, the adsorption isotherm should be determined atsubstantially the same temperature as used in actual operation, whichpreferably is room temperature orvordinary storage tank temperatures.

The second requirement for a satisfactory primary desorbing agent isthat it be capable of being displaced from the adsorbent by reasonableamounts of the secondary desorbing agent. This characteristic isdetermined according to the present invention by means of an arbitraryfactor termed the "adsorption index. We have found that organic liquidswhich have an adsorption index not greater than about 40 meet thisrequirement. Liquids which have an adsorption index of about 8-20 givebest results and therefore are preferred.

As used herein in both the description and claims, the adsorption indexof a compound may be dened as the apparent number of cubic centimetersof the compound adsorbed by one kilogram of the adsorbent when thelatter is in equilibrium with a solution consisting of the compound andthe secondary desorbing agent employed in the process, which solutioncontains 0.2 per cent of said compound by volume. For example, ifbenzene is under consideration as the primary desorbing agent andpentane is to be used as the secondary desorbing agent, then theadsorption index of benzene is the apparent number of cubic centimers ofbenzene adsorbed by one kilogram of the adsorbent in equilibrium with asolution consisting of 0.2 per cent benzene and 99.8 per cent pentane byvolume. The adsorption index thus is -a measure of the adsorbability ofthe primary desorbing agent from solution with the secondary agent, and,since adsorption is an equilibrium phenomenon, therefore is also ameasure of the ease with which the primary agent may -be displaced fromthe adsorbent by means of the secondary agent. The low concentration of0.2 per cent primary agent was chosen for specifying this index sincethe amount of secondary agent required to eiect removal of the irst isrelated more to the ease of desorption at low concentrations of primaryagent than at high concentrations.

6 It will be evident from the above definition that the "adsorptionindex is the ordinate value corresponding to an abscissa value of 0.2per cent primary liquid on the adsorption isotherm for a binary mixtureof primary and secondary liquids.

A convenient method of determining "adsorption index" comprises firstobtaining several points on the adsorption isotherm at lowconcentrations of the primary agent, preferably at concentrations belowabout 5 per cent. This may be done by contacting a measured volume oibinary mixture of known concentration with a given weight of adsorbentand determining the concentration of the solution after equilibrium hasbeen established. This procedure is carried out several times whilevarying the equlibrium concentration within the range below 5 per centprimary component, and in each case the amount of the component adsorbedis calculated from the original and iinal concentrations. In utilizingthis method for determining adsorption index," adsorption of thesecondary solvent and change in volume due to adsorption of the .primarysolvent are neglected, so that the calculated amount of primary solventadsorbed is an apparent amount rather than the actual amount. (Indetermining complete adsorption isotherms as shown in Fig. 1, a similarmethod also utilizing the apparent rather than actual adsorption isemployed.) The adsorption index then may be obtained, Without an actualdetermination at a concentration of 0.2 per cent, by plotting theexperimental data and extrapolating or interpolating to a concen.

tration of 0.2 per cent. Alternatively, since in A dilute solution theadsorption isotherm relationship is expressed with reasonable accuracyby the well-known equation of the Freundlich type:

M- KC" in which V is the volume of primary component adsorbed, M is theweight of adsorbent, C is the equilibrium concentration and K and N areconstants, this equation may be used to calculate the adsorption index.This is done by solving for the constants K and N from the knownexperimental data and then using these constants in the equation tocalculate the value of V when M equals one kilogram and C equals 0.2 percent by volume. The adsorption index should be determined Vatsubstantially the same temperalture as used 4in the process step ofdesorbing the primary agent by means of the secondary agent, whichpreferably is ordinary temperature.

In Fig. 2 of the accompanying drawings, adsorption isotherms obtained inthe above described manner for several mixtures of primary and secondaryliquids at room temperature with silica gel as the adsorbent are shown.In the following tabulation are listed "adsorption indexes obtained fromthe curves of Fig. 2. Adsorption indexes for methylcyclohexane inn-heptane and carbon tetrachloride in n-heptane are also listed:

Adsorption dex Primary Liquid Primary Liquid l Secondary Liquid 7 Sincean adsorption index of zero indicates that there is no difference in theadsorbabilities of the primary and secondary components, it is evidentthat the diierence in adsorbabilities of.

naphthenes, as exemplified by methylcyclohexane, and parains, asexemplied by n-heptane, is negligible insofar as the present process isconcerned. Either of these is a good example of a secondary desorbingagent. Since these types of hydrocarbons are 4not preferentiallyadsorbed from solution with aromatics at any concentration, they are notsuitable as primary agents. Monooleflnic hydrocarbons behave similarlyto naphthenic or paraiilnic hydrocarbons as far as the present inventionis concerned.

Benzene, with an adsorption index of 8 and being more strongly adsorbedthanhigh boiling aromatics as shown in Fig. 1 and discussed above, is asatisfactory primary desorbent. Toluene and xylene likewise meet therequirements, although their adsorption indexes are slightly lower thanthat for benzene and therefore are below the preferred range of 8-20.Other benzene derivatives also may be used as the primary K agent.

Ethylene dichloride, which has an index of 18 and which is more stronglyadsorbed than high boiling aromatics according to the definitionV setforth above, is an excellent primary agent. Ethyl chloride likewise issuitable. Many other halo-l genated hydrocarbons, including iodine,bromine and iluorlne derivatives, meet the requirements. Carbontetrachloride, however, is not as strongly adsorbed as the high boilingaromatics and therefore is not a satisfactory displacing agent therefor.In fact, this compound is suillciently poorly adsorbed that for thepresent purpose it is substantially equivalent to saturated hydrocarbonsand may be used as the secondary desorbing agent. Other organic liquidswhich are substantially equivalent to saturated hydrocarbons inadsorbability also may be employed as the secondary desorbent. For thepresent purpose it may be considered that any organic liquid which, inbinary solution with a relatively low boiling saturated hydrocarbon (forexample, pentane), has an "adsorption index less than about 2 issubstantially equivalent to saturated hydrocarbons and may be used asthe secondary desorbing liquid.

Various Oxy-hydrocarbons which are not too highly polar also may meetthe specifications for a satisfactory primary desorbent. However, asshown in the above tabulation, ethyl ether has an adsorption index"somewhat too high and requiresunreasonably large amounts of thesecondary agent to eiect-its desorption. Acetone and methylalcohol havesuch high indexes that, for practical purposes, it may be said thattheir removal cannot be effected by/means of the secondary desorbent.

One manner of practicing the invention comprises treating the chargestock with silica gelto adsorb aromatics, preferably by percolating .the

charge stock through the gel in a illtration zone,

passing the primary desorbing liquid through the gel in suillcientamount to desorb the aromatics,

and then passing sufllclent secondary desorbing liquid through the gelto bring its activity back to the desired value by desorption of theprimary agent. The eiuent from the iltration zone is segregated intodesired fractions, and the desorbents are separated and recovered fromthe fractions by distillation or any other suitable means. By propersegregation of the emuent stream, products varying widely in propertiesand ranging from non-aromatic to highly aromatic materials may beobtained. The refractive index of the eiilux serves as a convenientmeans of determining when properly to cut between the fractions.

In a preferred mode of operation, however, the invention includesseveral distinctive features which are highly advantageous. One' ofthese comprises diluting the charge stock with secondary desorbingagent, this preferably being a relatively low boiling saturatedhydrocarbon material such as pentane, and passing the solution ratherthan undiluted charge stock to the filter. Such dilution is not merelyfor the obvious purpose of facilitating filtration by reducing viscosityof the charge. In addition to this advantage, we have found thatdilution with certain proportions of the material used as secondarydesorbing liquid, or another solvent of the same type, improves theefciency of adsorbing aromatics from the charge. It appears that thenonaromatic hydrocarbons of the charge stock have a high solvency eiecton the aromatics, rendering them more dilcultly adsorbed from solution;

whereas the pentane (or its equivalent), although being completelymiscible with the aromatics, may be said to be a poorer solventtherefor, such as might be judged by differences in internal pressuresor deviations from the laws of ideal solution. Dilution with pentane orthe like thus has a tendency to render the charge stock aromatics moreeasily adsorbed. However, such dilution decreases the concentration ofaromatics in the charge and, in this respect, tends to have thelopposite effect. Therefore, there is a limit to the degree of dilutionfor increasing the eiliciency of adsorption. With usual charge stocks.this limit appears tol be at a ratio roughly in the neighborhood ofthree volumes of the liquid of secondary desorbing agent type to onevolume of charge stock. A ratio of at least 0.5:1 is desirable, and aratio of about 1.5:1 appears best considering effectiveness in renderingthe aromatics easily adsorbed and cost of recovering the diluent. Y

As previously stated. the invention in one form may be practiced for thepurpose of reducing the aromatic content of a charge stock rather thanof producing a substantially aromatic-free prod` uct, by omitting thestep of desorbing the primary agent with the secondary agent. In suchcase,

however, it is distinctly preferable that the charge stock be dilutedwith pentane or'the like as described above. We have found that gelcontaining adsorbed primary agent is Sufliciently active to efi'ectsubstantial removal of aromatics pro` vided the charge stock is properlydiluted with secondary liquid, but that the gel is too inactive toaccomplish this in a, dilution is omitted.

As another feature ofthe invention, a' step. wherein the adsorbent iswashed with secondary liquid, is introduced to follow the adsorptionstep. This serves t0 remove the charge hold-up from the interstices ofthe adsorbent; furthermore, since the secondary desorbing liquid isineffective to remove the adsorbed aromatics but is capable of desorbingnon-aromatics present in the adsorbate,` this step also serves toseparate adsorbed practical manner if the non-aromati-cs from thearomatics, thereby re-l sulting in a more complete separation of thecharge into aromatic and non-aromatic components.

For an adsorption process employing an expensive adsorbent such assilica gel to be commercially successful, it is necessary that the gelbe capable oi' `use through manyv cycles oi' operation black, viscous,highly aromatic odorous material containing about 1 per cent sulfur and1 per cent nitrogen, .ind its activity eventually drops to an uneconomiclevel, necessitating regeneration of a more severe type to eifectremoval of this material and bring the gel activity back to the desiredvalue. This more severe regeneration may be accomplished by passingthrough the gel a desorbing agent which is very strongly adsorbed, forexample, methanol or acetone, and then by blowing the gel at an elevatedtemperature, suitably G-180 C., with air until the adsorbed desorbent isremoved.

A further feature of the invention and one of distinct advantage inmaintaining activity of the adsorbent, thereby reducing the frequencywith series flow through the several zones; thus, as far as theadsorption step is concerned, this manner of operation is notessentially different from using a single zone. The aforementionedwashing step to remove hold-up and non-aromatics likewise is carried outwith the wash liquid (secondary desorbent type) flowing through thezones in series. However, parallel flow is used in the two other stepsof the cycle. Thus, fresh primary desorbing liquid is sent to andwithdrawn from each zone separately to desorb the aromatics therefrom.Likewise, fresh secondary agent is percolated through each zone todesorb the primary liquid in the same fashion. This manner of operationis adecided improvement in several respects. Of the aromatichydrocarbons adsorbed from the charge stock, the most highly aromatic(i. e., those containing the largest proportion of aromatic rings permolecule) are retained in the first section, those retained in thesecond section are less aromatic, those ,in the third section are ofstill lower aromaticity, etc. -Separate regeneration of each sectionthus permits the production of fractions of different aromaticities.Furthermore, considerably less primary rdesorbing agent is required toremove these fractions from each zone than would be the case if allfractions were washed through each succeeding zone, as occurs in seriesow desorption. In the step of desorbing the primary liquid by means ofthe secondary liquid, this manner of operation perantly in the firstzone and which is partiallyremovable by the primary desorbent, is notwashed into the succeeding zones and therefore does not have theopportunity to aii'ect the activity of adsorbent in these zones. Thus.the activity of adsorbent inl the first zone may drop to an uneconomiclevel after 50-100 cycles of operation, whereas adsorbent in the secondor third zone may be sumciently active throughout 200-400 cycles.Accordingly, adsorbent in the rst zone requires severe regeneration morefrequently than that in the other zones. The present feature permitsoccasional-complete revivification of that portion of total adsorbentrequiring it, without necessityfor subjecting all of the adsorbent tosevere regeneration, and, at the same time, appreciably reduces the timerequired in each cycle for regeneration by the desorbing liquids.

. In practicing the invention with a plurality of filtration zones asdescribed above, a series of lter drums or columns, or one columndivided into the desired number of vertical sections, may be utilized.Figs. 3A and 3-B in the accompanying drawings illustrate two suitablearrangements of apparatus, each ligure showing six filters byway ofillustration although a larger or smaller number of filters could beemployed in similar fashion. For simplicity, all the iiow lines whichwould be required in actual practice are not shown; for example, owlines for carrying out the desorption steps are omitted, it beingunderstood that desorption preferably is carried out for each filterseparately as describedabove. For purpose of illustration, it is assumedthat three iilter zones. are necessary to effect the desired adsorptionand that severe regeneration is required in the first zone after 50cycles. In Fig. 3A, charge is first passed through filters I-a, 2 and 3during the adsorption step of each cycle for 50 cycles. Then it is sentthrough filters l-b, 2 and 3 for 50 more cycles, during which period theadsorbent in a is subjected to severe regeneration. During the next 50cycles, charge again is passed through I--a, 2 and 3, and I-b issubjected to severe regeneration. Filters I-a and I-b are .usedalternately in this manner as the first filtration zone throughout theoperation. After say 200 cycles, the use of filter 21s discontinued, thecharge being passed alternately through I-a, 3 and 4 and I-b, 3 and 4,and filter 2 is subjected to severe regeneration. After 200 more cycles,for example, the ow is directed alternately through l-a,' 4 and 5 andI-b, 4 and 5 and the adsorbent in lter 3 is fully revivied; thereafterthrough I-a, 5 and 2 and I-b, 5 and 2; then l-a, 2 and 3 and I-b, 2 and3; etc. In the arrangement shown in Fig. 3-B, charge is first passedthrough I, 2 and 3 for 50 cycles; then through 2, 3 and 4 for the next50 cycles; 3, 4 and 5; 4, 5 and 6; 5, 6 and I; etc. As the use of eachfilter is discontinued, the adsorbent therein is completely regenerated.With decline i adsorbent activity, it may prove advantageous to employfour or more filters in series rather than three. These methods ofoperation permit maintenance of economic activity throughout prolongedoperatlon with a minimum of severe regeneration.

The following examples are illustrative although not necessarilylimitative of the invention:

'bottom sections only.

bottom filtration sections and containing 100.

grams of 28-200 mesh silica gel in each section was utilized in aprolonged cyclic operation. In each cycle 100 grams (108 ml.) of a.lubricating oil distillate derived froml a naphthenic base crude andhaving the properties tabulated below was diluted with 100 grams (160ml.) of pentane and the mixture was percolated by gravity flow in seriesthrough the three sections. After the charge mixture had passed throughthe column,

l2 with methanol and then blowing with hot air. At no other time duringthe prolonged operation was gel in the middle or bottom sectionssubjected to regeneration other than the reactivation by means of liquiddesorbing agents in accordance with the invention.

Pertinent data, including yields and properties of the filtrate andactivities of the gel corresponding to various cycles during theoperation, are given in the following tabulation:

Cycle C cle Cycle Cycle No. l NFI). 9 No. 257 No.258

Yield of iiltrate, per cent oi charge 49 53 62 56 Pro rties oi ltrate(Chargc) ematic vise. at 100 F., centistolres 104. 54. 71 58. 59Kinematle vise at 210F.,cmtlstokes. 7. 79 6. 38 6. 53

Viscosity 0 60 64 Refractive Index, m CJD.- 1. 5155 l. 4849 l. 4867 1.4910 1. 4863 Density, 21 0.!4 0-...- 0.930 .8891 .8936 Anilinc Point. O73. 4 Molecular Weight 354 383 382 t. per cent Aromatic Rin 17 Gelactivity at beginning o! cy For tl? section I 100 78 61 l 98 For ddle100 92 72 l 100 For bottom section.-...- 100 99 83 l 98 2 Gel in the topsection only was partially regenerated as follows:

hold-up was removed by passing 50 ml. of' petroleum ether through thethree sections in series, followed by an additional 25 ml. of petroleumether passed in series through the middle and ary desorbing agent. As ameasure of activity, 1

the ratio of the decrease in refractive index of a A This procedure wasAAdsorbate fractions then bgtgggp Activity tial regenen fue putin ionegenerat on Per cent Per cent After Cycle No. 3i 8l After Cycle No.84..- 64 77 After Cycle No. 152.. 52 82 After Cycle No. 2ll 46 72 'I'hetabulated data, show that eilicient operation in accordance with theinvention may be practiced with a given batch of adsorbent over a veryextended period.

standard oil on passing through the used gel to v the refractive indexdecrease for the same oil on passing through the original unused gelwasutilized, the activity being expressed as follows:

Percentactivity: f

Refractive index decrease Refractive index decrease with original gelThe aromatic fractions obtained throughout cycles 2-8 were compositedfor each section and the following test data were obtained on eachcomposite:

Thse data indicate that the aromatics themselves are fractionated in theoperation according to degree of aromaticity.

Example II The present example was carried out with substantially thesame operating conditions as in Example I. Charge stock from the samesource was used but the charge stock in this case had been treated with20 lbs. of concentrated sulfuric acid per bbL of oil. The followingtabulation shows data similar to those usted in the previ usl ex-Thesefresults indicate that the maidmum adamples: sorptlon of aromaticsis obtained at a dilution Cycle Cycle Cycle Cycle Cycle Cycle No. l No.12 No. 50 No. 96 No. 247 No.249

Yieid delcampe: cent orcharge 4s 07 e4 es 04 55 Pr ties ornitra.---. f or matic vise. at 100 F., centistokes-.. 58 .98 vxlnenetitlrlysc. at 210F., centistokes t.

incos t v Remedio Index c /D v 1.4905 1.4900 1.4907 1.4900 1.4005Density 21 C .9282 .8927 i mime remt, o. v7.0 Molecular wrm-- :404 384sez Wt. per ceiteAromaticfRiElgs 16 0 2. 2 G'lifcofiviffyang 1 go cy e'100 79 sa 49 51 |00 roi mifidie -MHf-f- 100 95 s2 7a e2 100 roi 00mm 1100 97 se s3 72 190- l Gel substantially fully regenerated b \washingwith methanol and blowing with hot air after cycle No. 248.

i Gel in the top section only was parti y regenerated as followsfActivity be- Activity ener fore partial partial regenregenerationeration Per cm Per cent After Cycle No. 98.-.- 58 71 After Cycle No.162... 39 63 After Cycle No. 221 37 62 The aromatic fractions obtainedthroughout -cycles `1-9 were composited for each section and thefollowing test data were obtained on each composite:

Aromatics composited from cycles 1-9 ilop Middle Bottom Section SectionSection Kinematicvise. at 100 F. centistakes i.. 323.8 231.6 278.7

i is at 210 F. cent- 10.00 11.35 11.10 Viscosity Index -220 -30 -89Refractive Index, 20 C./D l. 5501 l. 5288 Density, C./4 C 0. 0.9551Anilne Point, 24. 4 49. 8 Molecular Weight 371 348 Wt. per cent AromaticRings 66 40 Eample III The present example illustrates the effect ofdiluting the charge stock with solvent of the secondary type in order tofacilitate adsorptionof the aromatics. Several runs were inade, in eachof which 100 grams ofthe same charge stock as substantially differentfrom that used in the present example, the optimum dilution ratio may bedifferent.

The present invention is not necessarily limited to the use of silicagel as the specific adsorbent, since other adsorbents conformingsubstantially to silica gel in adsorptive properties also'may beutilized. The adsorbent should have a high selectivity for aromatichydrocarbons and should be capable of reactivation in accordance withthe invention. Various activated clays, for example, alumina or bauxite,although being less emcient than silica gel, meet these requirementssatisfactorily. When the above-described multiple section operation isused, it may be advantageous in some instances to use in the firstsection a cheaper and less effective adsorbent and employ a moreeffective adsorbent such as silica gel only in the other filtrationzones. This permits adsorbent in the first zone, whenever its activityhas declined to an uneconomic value, to be discarded. This may provemore economical than subjecting all of the The total filtrate in eachrun after pentane had y been removed was tested for refractive index,with results as follows:

Refractive index of diluent-free Dilution Ratio (Vol. of pentane pervol'. of chargev stock) filtrate v adsorbent to the occasional severeregeneration. The primary desorbing agents suitable for use with otheradsorbents will, in general, be those employed with silica gel, althoughthey will not necessarily be the same in all cases. In choosing aprimary desorbing liquid for use with a, specific adsorbent, it is onlynecessary to determine that the liquid in question meets the tworequirements, specified above, of being more strongly adsorbed than thearomatics by the particular adsorbent used, as determined by theadsorption isotherm, and of having an adsorption index less than about40. Even activated carbonLwhich is an organophilic adsorbent in contrastto silica gel which is hydrophilic, has been found to be capable offunctioning in a manner substantially equivalent to silica gel providedthe primary desorbing agent is chosenv as specified.

In choosing desorbents for practicing the process, itis desirable thatthey be so selected with respect to boiling point that they may be 15easily separated from the products and from each other by distillation.The desorbing agents em ployed, of course, should have no tendency toreact (e. g., polymerize) in the presence of the ad sorbent under theoperating conditions.

We claim:

Y 1. -A cyclic process for separating aromatic hydrocarbons from amixture of hydrocarbons containing the same and boiling mainly above 500F. which comprises treating saidk mixture with silica gel to adsorbaromatic hydrocarbons there--l from, washing the thus used adsorbentwith an organic primary liquid desorbing agent having an adsorbabilitysuch that, from binary solution of said aromatics and said desorbingagent,'the latter will be preferentially adsorbed by the adsorbent overa major portion o1' the concentration range and which is furthercharacterized by an adsorption index" not greater than about 40, therebyto displace aromatics from the adsorbent, and washing the adsorbent witha secondary desorbing agent comprising essentially a saturatehydrocarbon liquid adapted to eil'ect desorption of the primarydesorbing agent and to reactivate the adsorbent for re-use.

2. A cyclic process for separating aromatic hy drocarbons from a mixtureof hydrocarbons containing the same and fboilng mainly above 500 F.which comprises percolating said mixture through silica gel to adsorbaromatic hydrocar-` bons from said mixture, percolating through the thusused adsorbent an organic primary liquid desorbing agent having anadsorbability such that, from a binary solution of said aromatics andsaid desorbing agent, the latter will be preferentially adsorbed by theadsorbent over a major portion of the concentration range and which isfurther characterized by an "adsorption index not greater than about 40,thereby to displace aromatics from the adsorbent, and then percolatingthrough the adsorbent a secondary desorbing agent comprising essentiallya saturate hydrocarbon liquid adapted to effect desorption of theprimary desorbing agent and to reactivate the adsorbent for refuse.

3. The process defined in claim 2 wherein the charge stock is dilutedwith a saturate hydrocarbon liquid in amount eiective substantially to jimprove the adsorbability of aromatics from the charge, and theresulting mixture is percolated through the adsorbent to effectadsorption of the aromatics in the manner specified.

4. A cyclic process for separating aromatic hydrocarbons from a chargestock containing the same and boiling mainly above 500 F. whichcomprises diluting the charge stock with a saturate hydrocarbon liquid,said liquid, being used in amount effective substantially to improve theadsorbability of aromatics from the charge, adsorbing aromatics-from theresulting mixture by passing it in series flow through severalfiltration zones each of which contains silica gel, removing hold-up andadsorbed Anon-aromatics from the several zones by washing the`adsorbeht40, and then removing adsorbed primary desorbing agent from each zoneseparately by passing in parallel new through the several zones 'furtherquantities of saturate hydrocarbon liquid adapted as a secondarydesorbing agent to desor-b said primary desorbing agent from theadsorbent and to reactivate the adsorbent for reuse.

5. .A cyclic process 4for reducing the aromatic content of a chargestock containing aromatic hydrocarbons and boiling mainly above 500 F.which comprises diluting the charge stock with a relatively low boilingsolvent consisting essentially of pentane, said solvent being used inamount effective substantially to improve the adsorbability of aromaticsfrom the charge, treating the resulting mixture with' silica gel toadsorb aromatic hydrocarbons therefrom, and washing the thus usedadsorbent with an organic liquid desorbing agent having an adsorbabilitysuch that, from binary solution of said aromatics and said desorbingagent, the latter will -be preferentially adsorbed by the adsorbent overa major portion of the concentration range and which is furthercharacterized by an absorption index not greater than about 4.0 inbinary solution with pentane, thereby to displace aromatics from theadsorbent and reactivate the adsorbent Ifor -re-use.

6. A process for reducing the aromatic content of a charge stockcontaining aromatic hydrocarbons and boiling mainly above 500 F. whichcomprises a continual cyclic operation wherein in each cycle the chargestock is diluted with a saturate hydrocarbon liquid in amount eiectivesubstantially to improve the adsorbability of aromatics from the charge,the resulting mixture is contacted with silica gel to adsorb aromatichydrocarbons therefrom, and the thus used adsorbent is contacted with anorganic liquid desorbing agent having an adsorbability such that. from abinary solution of said aromatics and said desorbing agent, the latterwill be preferentially adsorbed by the adsorbent over a major portionVof the concentration range and which is further characterized by an"adsorption index" not greater than about 40 in binary solution withpentane, thereby to displace aromatics and reactivate the adsorbent forre-use.

7. The process delined in claim 2 wherein-the primary desorbing agent isbenzene and the secondary desorbing agent is a relatively low bollingsaturate hydrocarbon material.

8. The process deiined in claim 2 wherein the primary desorbing agent isethylene dichloride and the secondary desorbing agent is a relativelylow boiling saturate hydrocarbon material.

9. The process defined in claim 5 wherein the desorbing a'gent isbenzene;

10. The process deiined in claim 5 wherein the desorbing agent isethylene dichloride.

11. The process defined in claim 6 wherein the desorbing agent isbenzene.

l2. The process defined in claim 6 wherein the 'ilein With fllrtherquantity 0f saturate hy- 05 desorbing agent is ethylene dichloride.

drooarbon liquid, rmoving-adsorbed ,aromatics from each zone separatelyby passingA`in^parallel`` ow through the several zones an organicprimary liquid desorbing agent having an adsorbability such that, from abinary solution of the aromatics and said primary desorbing agent, the

latter will lbe preferentially adsorbed by said adsorbent over a majorportion of the concentration range and which' is furthercharacterized byan "adsorption index" not greater than about primary liquid desorbingagent is benzene.

I4.`"'I'l'lerproc`ess defined in claim 1 wherein the primary liquiddesorbing agent is ethylene dichloride.

ALFRED E. HIRSCHLER.. MOSES ROBERT LIPKIN.

(References on following page) 17 REFERENCES onnn The followingreferences are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,678,298 Patrick -..July 24,1928 1,868,581 Miller July 26, 1932 OTHER REFERENCES Mair et al.,Separation of Petroleum Silica Gel." Oil amdv Gas Journal, Sept. 19,1935, pages 29-32. (Copy in 196.147.)

